KR20090115232A - Method and apparatus for mitigating interference in multicarrier modulation systems - Google Patents

Abstract

A method and apparatus for mitigating the effect of adjacent channel interference in a multicarrier modulation system is provided. The method includes receiving (402) an encoded signal over multiple subcarriers at different frequencies. The signal includes a plurality of pilot symbols and data symbols modulated onto the subcarriers using a modulation technique. Further, the method includes: grouping (404) the subcarriers into multiple sets of subcarriers based on their frequencies, wherein each set includes one or more subcarriers; estimating (406), for each set of subcarriers, a noise value associated with at least a portion of the pilot symbols received over subcarriers included in the set; and generating (408) a decoded signal comprising a plurality of decoded data bits, using the estimated noise values.

Description

TECHNICAL AND APPARATUS FOR MITIGATING INTERFERENCE IN MULTICARRIER MODULATION SYSTEMS

TECHNICAL FIELD The technical field generally relates to communication systems, and more particularly, to a method and apparatus for mitigating interference in multicarrier modulation systems.

Multicarrier modulation (MCM) systems used to transmit signals using multiple subcarriers over a channel, such as using Orthogonal Frequency Division Multiplexing (OFDM), provide efficient bandwidth utilization and intersymbol interference. Performs better resistance to s where inter-symbol interference occurs due to spreading of signals and high rate symbol transmission. In multicarrier modulation systems, digital signals are used to convey information from a first position to a second position across a transmission medium, also called a Radio Frequency (RF) channel, comprised of a particular radio frequency or band of frequencies. . Examples of information include, but are not limited to, digitized text, digitized video, and digitized audio. The transmitter disposed at the first position transmits the digital signal and the receiver disposed at the second position receives the transmitted digital signal.

In MCM systems, the digital signal is subdivided into multiple bit streams, each bit stream being encoded into data symbols. Examples of encoded data symbols include binary phase-shift keying (BPSK) symbols, 16 quadrature amplitude modulation (QAM) symbols, 64 QAM symbols and quadrature phase-shift keying (QPSK) symbols, but with this It is not limited. Each bit stream encoded in the data symbols forms a symbol stream. Each symbol stream is modulated onto a subcarrier before transmission. In addition, one or more pilot symbols are typically inserted in the respective symbol streams to perform coherent reception. These pilot symbols can also be used to evaluate the quality of the digital signal received at the receiver.

For the transmission of complex MCM digital signals, the channel bandwidth for the RF channel is generally subdivided into subcarriers of the same bandwidth. The subcarriers are modulated into symbol streams and combined into a composite digital signal, which is transmitted from the first position to the second position. In the second position, the receiver demodulates the composite digital signal and detects individual subcarriers. Individual subcarriers are processed and information is recovered from the digital signal.

In general, the quality of a composite digital signal is degraded by noise present across the RF channel. Apart from the deterioration in quality suffered by the noise present across the RF channel, the received composite digital signal is also sent from transmitters transmitting at the same frequency as the target signal but with the target of different physical locations or other digital signals transmitted. It is sensitive to interference from transmitters transmitting on channels at frequencies adjacent to the signal.

Adjacent channel interference (ACI) is a characteristic of frequency division multiplex (FDM) systems, including MCM systems. ACI is generally generated due to the non-ideal nature of the filters, where the non-ideal filters of the transmitter cannot remove all emissions outside their intended channel, so that some undesired energy is present in the receiver of the adjacent channel. . In addition, external subcarriers present in the channel in MCM systems are more likely to interfere with interference from signals present in adjacent channels (compared to internal subcarriers present in the channel) because they are closer to the interference source in terms of frequency. be sensitive. In scenarios where co-channel interference exists, the central subcarriers are typically more sensitive to the interference source if the interferer has a bandwidth less than the bandwidth of the desired signal.

One common method for mitigating co-channel or adjacent interference is by using interleaving to spread clustered errors within certain subcarriers over a coded block. Interleaving is a process that is equally distributed across coded blocks when the receiver reorders the data before the receiver performs forward error correction if the transmission order of the data in the digital signal is modified so that a cluster of errors is caused by the channel. to be. Another conventional method for mitigating adjacent channel interference uses a more acceptable type of signal arrangement in external subcarriers such as QPSK to mitigate the interference caused by signals on adjacent channels. Thus, because such modulation is more tolerant to interference, the overall performance is improved.

로부터 전송된 심볼들, 및 수신된 심볼(r)을 사용한 이진 위상 시프트 키잉(BPSK) 변조에 대해, LLR(

)은 가능한 심볼 가설(

및

)의 추후 가능성들의 비율의 자연적인 로그로서 정의된다. 여기서 복합 신호에 존재하는 노이즈가 변수(

)를 가진 부가적인 화이트 가우시안 노이즈이고, 각각의 심볼이 똑같이 하기가 가능하다:Interference can cause errors in the decoding of the composite digital signal. In some receivers, decoding of the composite digital signal is performed by forward error correction (FEC) decoders. Modern FEC decoders decode soft decision inputs to improve performance, and the soft decision inputs provide the decoder with additional information that can be used in the decoding process. One soft decision input based on a maximum later (MAP) decision is called a log-likelihood ratio (LLR). For example, the alphabet

For symbols transmitted from and binary phase shift keying (BPSK) modulation using received symbol r, LLR (

) Is a possible symbol hypothesis (

And

Is defined as the natural logarithm of the ratio of future possibilities. Where the noise present in the composite signal

It is an additional white Gaussian noise with), and it is possible for each symbol to do the same:

(1)

(One)

Similar to what can be seen by equation (1), it can be seen that for all array types, the generality that the LLR value is inversely related to the noise of the composite signal. Typically, the LLR is calculated by providing a noise estimate that is achieved by taking the average value of the entire composite digital signal. However, the average value of the noise of the entire composite digital signal may lead to inaccurate determination by the FEC decoder when an attempt is made to mitigate the interference effect due to adjacent channels and / or co-channel interference sources.

Thus, there is a need for a method and apparatus for mitigating interference in MCM systems that address at least some disadvantages of past and current interference mitigation techniques.

The accompanying drawings, in which like reference numerals refer to the same or functionally similar elements, further illustrate various embodiments of the concepts comprising the claimed invention, which are incorporated in and form a part of the specification, together with the following detailed description, of which Used to illustrate various principles and advantages.

1 is a block diagram of a communication system, and some embodiments are implemented at a receiver of the system.

2 is a block diagram of a communication system, and some embodiments are implemented in a receiver of the system.

3 is a symbol diagram of a prior art composite signal transmitted from a transmitter of the system shown in FIG.

4 is a flow chart illustrating a method for mitigating interferences in MCM systems in accordance with some embodiments.

5 is a block diagram of a symbol demodulator in accordance with some embodiments.

6 is a symbol diagram of a composite signal received and processed in accordance with some embodiments.

Those skilled in the art will recognize that elements of the figures have been shown for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some elements in the figures may be exaggerated with respect to other elements to improve understanding of the various embodiments. In addition, the description and drawings do not necessarily require the order shown. Apparatus and method components are represented by conventional symbols in the drawings where appropriate, and the drawings are understood to explain various embodiments in order not to obscure the disclosure with items that would be apparent to those skilled in the art having the benefit of the description herein. Only certain items suitable for doing so are shown. Thus, for simplicity and clarity of illustration, it will be appreciated that common and well understood elements useful or necessary for commercially viable embodiments may not be disclosed to lessen the clarity of these various embodiments.

In general, provided are a method and apparatus for mitigating interference in an MCM system in accordance with various embodiments. The method includes receiving an encoded signal on multiple subcarriers at different frequencies. The signal includes a number of pilot symbols and data symbols modulated on the subcarriers using suitable modulation techniques. In addition, the method includes grouping the subcarriers into multiple sets of subcarriers based on frequencies, wherein each set includes one or more subcarriers. The method also includes evaluating a noise value associated with at least some of the pilot symbols received on the subcarriers included in the set for each set of subcarriers. The estimated noise power value (called noise value here simply evaluated) includes both the additional white Gaussian noise and the interference on which the composite signal is affected. In addition, the method includes generating a decoded signal comprising a plurality of decoded data bits using the estimated noise values.

The apparatus includes a receiver apparatus and a processing device. The receiver receives an encoded signal over multiple subcarriers at different frequencies, where the signal comprises a plurality of pilot symbols and data symbols modulated on the subcarriers using a modulation technique. The processing device comprises: grouping subcarriers into sets of multiple subcarriers based on frequencies; Evaluating for each set of subcarriers a noise value associated with at least some of the pilot symbols received on the subcarriers included in the set; And using the evaluated noise values to produce a decoded signal comprising a plurality of decoded data bits.

The noise evaluation value is calculated on a subcarrier basis and / or for a small group of subcarriers. The noise estimate value is used to calculate an LLR value that can provide additional information to FEC decoders to improve coding performance. According to embodiments, the FEC decoder is provided with a more detailed knowledge of where interference occurs through the magnitude of noise estimates per group of subcarriers and / or subcarriers. The additional information provided to the FEC raises a better possibility of modifying the received signal. Those skilled in the art will recognize that the above recognized advantages and other advantages described herein are merely illustrated and are not intended to be exhaustive of all the advantages of the various embodiments.

With reference now to the drawings, and with reference to FIG. 1, a specific example of operation using a multicarrier modulation system is shown and illustrated to provide a illustration, but not an exhaustive example for facilitating this description. It is generally indicated by 100. However, those skilled in the art will recognize that the features of this illustration are not features of the invention itself and that the guidelines presented herein may be applied to various alternative settings. For example, because the guidelines described do not depend on any particular platform, these instructions are based on BPSK, QPSK, least-shift keying (MSK), offset quadrature phase-shift keying, although the 16-QAM implementation is described herein. (OQPSK), and Quadrature Amplitude Modulation (QAM), but can be applied to any type of MCM system with one or more subcarriers modulated, but not limited to. As such, other alternative implementations using other types of MCM systems are within the scope of various guidelines devised and described.

Referring now to the illustrated MCM system 100, the MCM system 100 includes a transmitter 102 and a receiver 104. The transmitter 102 and receiver 104 may be part of wireless communication devices, examples of which include, but are not limited to, mobile phones, laptops, and the like. These wireless communication devices can communicate with each other via MCM systems, examples of which are high performance data (HPD), TIA902.BAAB high speed data / scalable adaptive modulation (HSD / SAM), TETRA 2, and other using OFDM concepts. Include systems.

The transmitter 102 includes an information source 106, a serial-to-parallel converter 108, a symbol converter 110, and processing blocks 112, 114, 116. The processing blocks 112, 114, 116 are similar in functionality. For example, processing block 112 includes a synchronization / pilot symbol insertion block 118, a pulse shaping filter block 120, and a complex mixer block 122. In addition, the transmitter 102 includes a summing block 124, an imaginary-part block 126, and a real-part block 128. Elements 112, 114, 116, 124, 126, 128 are functional blocks that can be executed using any suitable processing device, such as one or more later described processing devices. Finally, the transmitter 102 includes a quad upconverter 130, an amplifier block 132 and an antenna (collectively referred to herein as a transmitter device) that upconverts the signal from the baseband to the radio carrier frequency for transmission over the RF channel. 134). Receiver 104 includes antenna 136 and additional elements described below with reference to FIG.

MCM system 100 is used to transmit digital signals across an RF channel. In an RF channel, a digital signal is transmitted on multiple subcarriers. Each subcarrier is modulated with a specific offset carrier frequency. In operation, the information source 106 sends information in the form of a bit stream to the serial-to-parallel converter 108 at a rate of 'B' bits per second, for example. Examples of information include, but are not limited to, digitized text, digitized video, and digitized audio. Serial-to-parallel converter 108 converts the digital information into the 'M' numbers of the other bit streams. In addition, each 'M' bit stream corresponds to a specific subcarrier. Therefore, there are 'M' subcarriers allocated for 'M' bit streams. In addition, serial-to-parallel converter 108 sends each bit stream to symbol converter 110, which converts each bit stream into a stream of QAM symbols. In this embodiment, symbol converter 110 converts digital information into 16 QAM symbols. In 16 QAM symbols, each QAM symbol may represent a 4 bit word. In addition, each QAM symbol can be represented in a Cartesian coordinate system, where the real part of the QAM symbol is shown along one axis and the imaginary part of the QAM symbol can be shown along the other axis.

The symbol converter 110 transmits QAM symbols corresponding to other bit streams (eg, d ₁ , d _2, and d _M , respectively) to the processing blocks 112, 114, 116. Each processing block corresponds to a specific subcarrier, where only three said processing blocks are shown for simplicity of illustration. In addition, because the processing blocks 112, 114, 116 are similar in functionality, the functionality of each processing block will be described with respect to the processing block 112. Processing block 112 corresponds to subcarrier 1. At processing block 112, synchronization / pilot symbol insertion block 118 inserts synchronization (" sync ") and pilot symbols into the stream of QAM symbols to form a composite symbol stream. Synchronization symbols are used to perform coherent reception of signals transmitted by receiver 104. The pilot symbols are used by the receiver 104 to evaluate the effects of the channel on the received signal in comparison with the signal transmitted from the transmitter 102 and to evaluate the quality of the signal received at the receiver 104.

Synchronization / pilot symbol insertion block 118 is used in the pulse symbol filter block 120 to limit the spectrum of the subcarrier to minimize interference of adjacent subcarriers (e.g., in processing blocks 112, 114, and 116). S ₁ , S ₂ and S _M ) respectively. Complex mixer block 122 modulates the composite symbol stream with the subcarrier signal at a particular offset frequency (eg, f ₁ , f _2, and f _M for processing blocks 112, 114, and 116, respectively). Similarly, the bit stream is processed by processing blocks 114 and 116 to produce corresponding composite symbol streams.

The composite signal is generated by a summing block 124 that adds all of the composite symbol streams from the processing blocks 112, 114, 116. The composite signal is separated into real and imaginary components by using imaginary block 126 and real block 128, respectively, and forwarded to quad upconverter block 130. Quad up-converter block 130 mixes the real and imaginary components into the radio carrier frequency and combines them into the composite signal. In addition, the composite signal from quad upconverter 130 is transmitted to amplifier 132. The amplifier 132 amplifies the power of the composite signal before transmission. In addition, the composite signal 140 is transmitted via the antenna 134 to the receiver 104 across the RF channel. The illustrated composite signal 140 is described in more detail below with reference to FIG. 3. At the receiver 104 the antenna 136 receives and processes the transmitted composite signal to extract data bit streams from the composite signal according to the instructions herein.

Referring to FIG. 2, system 100 is shown in an enlarged view of the depicted structure of receiver 104 in accordance with some embodiments. As described above, the antenna 136 of the receiver 104 receives the composite signal transmitted by the transmitter 102, the transmitted composite signal is indicated as 140 in FIG. 1 and the received composite signal is 240 in FIG. 2. It is expressed as The received composite signal 240 shown is described in more detail below with reference to FIG. Both signals (i.e. 140 and 240) identify the composite signal transmitted from transmitter 102, but show the effect of signal-to-noise and interference when traveling across the RF channel from transmitter 102 to receiver 104. It is noted that other reference numbers are used to make the bet.

Receiver 104 includes preselector filter 202 and quadrature down-converter 204 (collectively referred to herein as a receiver device for downconverting composite signal 240 from a wireless carrier frequency to baseband), subcarrier receivers. 206, 208, 210, 212, and symbol demodulator 214. Elements 206, 208, 210, 212, 214 are functional block diagrams that may be implemented using any suitable processing devices, such as one or more processing devices described later.

In operation, after receiving the composite signal 240 at the antenna 136, the composite signal is sent to the preselector filter 202. Preselector filter 202 is a tunable filter that can be tuned to receive a composite signal of a particular frequency. In addition, the preselector filter 202 sends the composite signal to the quadrature down-converter 204. Quadrature down-converter 204 converts the composite signal at the wireless carrier frequency level into a complex composite baseband signal centered at 0 Hz. After switching to the baseband level, the composite signal is sent to the subcarrier receivers 206, 208, 210, 212. Subcarrier receivers 206, 208, 210, and 212 separate the downconverted composite signal into other subcarriers based on their frequency offset. Subcarrier receivers 206, 208, 210, and 212 have similar functionality. Each subcarrier receiver generally recovers a symbol stream from another subcarrier, and only four said subcarrier receivers are shown for simplicity of illustration. The composite symbol stream from the subcarrier receivers 206, 208, 210, 212 is sent to the symbol demodulator 214. The symbol demodulator 214 processes the complex symbol stream to recover the bit stream sent by the transmitter 102 in accordance with the instructions herein.

Referring now to FIG. 3, a symbol diagram of the transmitted composite signal 140 is shown. The composite signal 140 includes sixteen subcarriers 302, 304, 306, 308, 310, 312, 314, 316, 318, 320, 322, 324, 326, 328, 330, 332. Each subcarrier may include data symbols, pilot symbols and synchronization symbols, the data symbols are shown as boxes without hash marks, and the pilot and synchronization symbols are shown as boxes containing hash marks. . Synchronization symbols are used to allow the receiver 104 to coordinate the reception of the transmitted signals in the correct order using time synchronization. Pilot symbols are used to evaluate the effects of the channel on the received composite signal and to evaluate the noise level in the received composite signal. For example, subcarrier 332 includes synchronization symbol 334. Subcarrier 328 includes pilot symbols 344, 346, 350. Subcarrier 324 includes data symbol 340. Subcarrier 322 includes pilot symbol 348. Subcarrier 320 includes pilot symbols 338 and 342, and subcarrier 314 includes data symbol 336.

Typically, in an FDM system where multiple subcarriers are used (in MCM systems), the outer subcarriers, for example 302, 304, 330 and 332, are adjacent to these adjacent subcarriers such as 314, 316 and 318. Proximity to the external subcarriers of the channels suffers more from interference from adjacent channels. Interference of RF channels can lead to false reception. In order to facilitate proper reception of the composite signal and thus mitigate the effects of various interference sources (and other noise) on the composite signal during transmission, the receiver evaluates the noise level for use in interference / noise mitigation techniques. The noise level in the received composite signal can be estimated by first using the surrounding pilot symbols to evaluate the target pilot symbol value using, for example, pilot interpolation processing. Then, by comparing the known transmitted pilot symbols with the evaluated pilot symbols received at the receiver, an estimate of the noise present in the temporary symbols in the channel can be obtained. This process may be repeated for additional pilots and results averaged together to form complex noise estimates such as those according to the guidelines herein.

Referring now to FIG. 4, a flowchart illustrating a method for mitigating interference of MCM systems is shown in accordance with some embodiments. For describing the method, reference is made to FIGS. 2, 5 and 6 although the method may also be implemented with reference to any other suitable embodiment. In addition, the method may include a different number of steps than shown in FIG.

At 402, an encoded signal is received on multiple subcarriers at different frequencies. The signal includes a number of pilot symbols and data symbols modulated on subcarriers using a modulation technique. The signal may be, for example, a composite signal 240 received by the receiver 104. At 404, subcarriers are grouped into multiple sets of subcarriers based on frequencies. Each set of subcarriers includes one or more subcarriers, and in general, but not necessarily, subcarriers grouped together in the set have adjacent subcarrier frequencies.

At 406, a noise value associated with at least some of the pilot symbols received on the subcarriers included in each set is evaluated. If the received pilot symbol is modeled as follows:

(2)

(2)

는 수신된 파일롯 심볼 수(i)이고,

는 전송된 파일롯 심볼의 크기이고,

는 파일롯 위치(i)에서 채널 응답이고, n은 노이즈 및 간섭을 나타내어, 노이즈 평가값은 하기 방정식을 사용하여 평가될 수 있다:here

Is the number of received pilot symbols (i),

Is the size of the transmitted pilot symbol,

Is the channel response at pilot position (i) and n represents noise and interference so that the noise estimate can be evaluated using the following equation:

(3)

(3)

는 또한 간단히 노이즈 값(여기서 노이즈 파워 값이 부가적인 화이트 가우시안 노이즈 및 간섭으로부터의 조성물들을 포함하는 것으로 이해되어야 한다)이라 불리는 평가된 노이즈 파워 값이고,

는 전송된 파일롯 심볼 수(i)의 크기이고,

는 파일롯 심볼 위치(i)에서 채널 응답의 평가값이고,

는 파일롯 보간 설계 파라미터들로부터 계산된 상수이고, N은 평균에 사용된 파일롯 심볼들의 총 수이다. 여기서,

는 노이즈 평가에 사용된 각각의 세트에 포함된 서브캐리어들을 통해 수신된 파일롯 심볼들 부분이고

는 파일롯 심볼 위치들에서 파일롯 보간에 의해 제공된 채널 평가값이다.here

Is also simply an estimated noise power value, referred to as a noise value, where the noise power value includes compositions from additional white Gaussian noise and interference,

Is the size of the number of transmitted pilot symbols (i),

Is an estimate of the channel response at pilot symbol position (i),

Is a constant calculated from the pilot interpolation design parameters, and N is the total number of pilot symbols used for the average. here,

Is the portion of pilot symbols received on the subcarriers included in each set used for noise evaluation

Is the channel estimate provided by pilot interpolation at pilot symbol positions.

)이 이들 4개의 서브캐리어들 내 적어도 몇몇의 파일롯 심볼들을 사용하여 결정되는 서브캐리어들(302, 304, 306, 308)을 포함한다. 마찬가지로, 제 2 노이즈 평가 값(

)은 서브캐리어들(310, 312, 314, 316, 318, 320, 322, 324)을 포함하는 서브캐리어들의 제 2 그룹으로부터 파일롯 심볼들을 사용하여 결정되고, 제 3 노이즈 평가 값(

)은 서브캐리어들(326, 328, 330, 332)을 포함하는 서브캐리어들의 제 3 그룹으로부터 파일롯 심볼들을 사용하여 결정된다. 이런 실시예에서, 외부 서브캐리어들은 함께 그룹화되고 외부 서브캐리어들에 대응하는 노이즈 평가값들(예를 들어

및

)은 내부 서브캐리어들에 대응하는 노이즈 평가값(예를 들어,

)로부터 독립적으로 결정되는데, 그 이유는 특정 주파수 외부 서브캐리어들에서 보다 클 수 있다는 것이 예상되기 때문이다. 임의의 다른 적당한 파라미터들은 서브캐리어들을 그룹화하는 방법을 결정하고 각각의 세트에서 서브캐리어들의 수를 결정하기 위해 사용될 수 있다. 그러나, 이용 가능한 평균을 형성하기 위하여 충분히 큰 수의 샘플들을 계속 인에이블링하면서, 한 그룹에서 서브캐리어들의 수를 가능한 한 작게 하는 것이 일반적으로 바람직하다. 게다가, 실시예들은 그룹화가 정적으로 유지되거나 신호가 수신될 때 동적으로 조절되는 경우가 고안될 수 있다.Referring briefly to FIG. 6, a slot diagram of the received signal 240 is shown. The grouping of 16 subcarriers includes three sets of subcarriers (or groups in this example). The first group is the first noise evaluation value (

) Includes subcarriers 302, 304, 306, 308 that are determined using at least some pilot symbols in these four subcarriers. Similarly, the second noise evaluation value (

) Is determined using pilot symbols from a second group of subcarriers comprising subcarriers 310, 312, 314, 316, 318, 320, 322, 324, and a third noise estimate value (

) Is determined using pilot symbols from a third group of subcarriers comprising subcarriers 326, 328, 330, 332. In this embodiment, the external subcarriers are grouped together and corresponding to noise estimates (eg, corresponding to the external subcarriers).

And

) Is a noise estimate corresponding to the internal subcarriers (e.g.,

Is independently determined, since it is expected that it may be larger at certain frequency outward subcarriers. Any other suitable parameters can be used to determine how to group the subcarriers and to determine the number of subcarriers in each set. However, it is generally desirable to keep the number of subcarriers in one group as small as possible while continuing to enable a sufficiently large number of samples to form an available average. In addition, embodiments may be devised where the grouping remains static or dynamically adjusted when a signal is received.

At 408, a decoded signal comprising a plurality of decoded data bits is generated using an appropriate equation (determined based on the modulation technique used) by applying multiple evaluation noise values calculated using equation (3). In particular, a number of received data bits are generated from the received data symbols and for each received data bit, an evaluation of the bit is made and a reliability measure is determined in association with the evaluated bit value. The reliability measure is a function of the estimated noise value corresponding to the set of subcarriers in which the data bit contains the received subcarrier.

)에 역으로 비례하고 각각의 수신된 데이터 비트에 대해 노이즈 평가값 및 연관된 LLR이 결정되는 것을 방정식(1)으로부터 알 수 있고, 이것은 하기 유도물들을 통해 도시된 바와 같은 16QAM을 포함하는 다른 변조 기술들에 대해 진실을 유지 한다. 게다가, 노이즈 평가 측정은 데이터 비트가 수신된 서브캐리어를 포함하는 서브캐리어들의 세트에 대응하는 노이즈 값들을 평균화하는 것에 기초하고 LLR은 변조 기술에 기초하는 방정식을 사용하여 평가된다.If the receiver includes an FEC decoder, the plurality of received data bits are decoded using an associated reliability measure that includes a log-likelihood ratio to produce a decoded signal. LLR refers to a measure of certainty where the value of a bit evaluated for a received data bit is the actual value of the corresponding transmitted data bit. LLR is the noise estimate

It can be seen from equation (1) that the noise estimate and associated LLR is determined for each received data bit inversely proportional to), which is another modulation technique including 16QAM as shown through the following derivatives. Keep the truth about them. In addition, the noise evaluation measurement is based on averaging noise values corresponding to the set of subcarriers that the data carrier contains the received subcarrier and the LLR is evaluated using an equation based on the modulation technique.

으로부터 선택된다. 각각의 이들 심볼들은 2비트의 정보를 표현한다. 예를 들어,

의 비트 패턴이 심볼 +3에 대응하고,

가 +1의 심볼에 대응하고,

가 -3의 심볼에 대응하고

가 심볼 -1에 대응한다고 하자. 그러나, 다른 비트 대 심볼 맵핑들이 똑같이 유효한 것이 주지되어야 한다.For example, for 16QAM modulation, a pair of symbols are transmitted for each symbol instant, and the pair of symbols are on the quadrature (Q) portion of the carrier and symbols in the in-phase (I) of the carrier. Are symbols. The symbols are t

Is selected from. Each of these symbols represents two bits of information. E.g,

The bit pattern of corresponds to symbol +3,

Corresponds to a symbol of +1,

Corresponds to a symbol of -3

Assume that corresponds to symbol -1. However, it should be noted that other bit to symbol mappings are equally valid.

은 신호의 동위상 및 쿼드러쳐 부분들 내에서 각각의 비트에 대한 가능한 심볼 가정(

,

, 및

)의 추후 가능성들의 비율의 자연 로그로서 수신된 심볼(r) 및 전송된 심볼(t)에 의하여 정의된다:Both the transmitted symbol t and the received symbol r are represented as complex numbers, where the in-phase portion of the signal is represented as a real part of the complex number and the quadrature portion of the signal is a complex imaginary number. Note that it is expressed as a portion. Given these assumptions, the log-likelihood ratio (LLR)

Is the possible symbol assumption for each bit in the in-phase and quadrature portions of the signal (

,

, And

Is defined by the received symbol r and the transmitted symbol t as the natural logarithm of the ratio of future possibilities of

는 수신된 신호의 동위상 부분 상 비트(b₀)에 대응하는 LLR이고,

는 수신된 신호의 동위상 부분상 비트(b₁)에 대응하는 LLR이고, 는 수신된 신호의 쿼드러쳐 부분 상 비트(b₀)에 대응하는 LLR이고,

는 수신된 신호의 쿼드러쳐 부분상 비트(b₁)에 대응하는 LLR이다. 부가적으로, 오퍼레이터 "real()"는 복소수 수신 심볼의 실수부를 추출하고 "imag()" 오퍼레이터는 복소수 수신 심볼의 허수부를 추출한다.here

Is the LLR corresponding to bit b _{0 on} the in-phase portion of the received signal,

Is the LLR corresponding to bit b _{1 on} the in-phase portion of the received signal, Is the LLR corresponding to bit b _{0 on} the quadrature portion of the received signal,

Is the LLR corresponding to bit b _{1 on} the quadrature portion of the received signal. Additionally, the operator "real ()" extracts the real part of the complex received symbol and the "imag ()" operator extracts the imaginary part of the complex received symbol.

) 측면에서 추후 확률들, 및 주어진 심볼이 전송된

:

인 확률을 표현하는 베이즈 정리의 혼합 형태를 사용하자. 게다가, 각각의 심볼이 똑같이 가능하다는 것을 가정 하자, 즉

를 가정하면, 우리는 다음과 같이 LLR들을 다시 쓸 수 있다:Conditional probability density function (

Later probabilities, and given symbol is transmitted

:

Use a mixed form of Bayes' theorem to express the probability of In addition, suppose that each symbol is equally possible, ie

Suppose we can rewrite the LLRs as follows:

을 가진 간섭을 포함하고, 이것은 조건적 확률 밀도 함수

가 또한 동일한 변수를 가진 가우시안인 것을 유발한다. 이런 가정으로, LLR들은 다음과 같이 쓰여진다.An additional assumption of this derivation is that the noise present in the composite signal adds additional white Gaussian noise and

Includes interference with, which is a conditional probability density function

Also causes Gaussian to have the same variable. With this assumption, LLRs are written as

를 사용하여, LLR들이 다음과 같이 단순화된다는 것을 알 수 있다:Finally, approximation ln

Using, we can see that the LLRs are simplified as follows:

The derivations for 16QAM modulation show that the LLR is inversely proportional to the noise estimate. The calculation of noise estimate values for the encoded signal may be done on a subcarrier basis or for a small group of subcarriers. For example, the noise estimate of the subcarrier 328 may be calculated independently using the pilot symbols 644, 646, 650. The bits received on subcarrier 328 are then evaluated only for subcarrier 328 or a group of subcarriers comprising subcarrier 328, eg, the third of the subcarriers described above with reference to FIG. 6. It is evaluated using the LLR value calculated using the noise value evaluated for the group.

As mentioned previously, the outer subcarriers (eg, 302, 304, 330, and 332) are adjacent to the outer subcarriers of these adjacent channels compared to the inner subcarriers such as 314, 316, and 318. Greater interference from adjacent channels. As a result, the outer subcarriers have a correspondingly higher noise estimate when compared to the inner subcarriers, which are LLRs for the bits received over the outer subcarriers since the LLR value is inversely proportional to the noise estimate. Lower the values. Lower LLR values are preferably applied to bits received on the outer subcarriers according to the instructions herein. Similarly, the inner subcarriers 314, 316, 318 have correspondingly lower noise evaluation values compared to the outer subcarriers, which results in higher LLR values applied to the bits received on the inner subcarriers. Thus, instead of using a single noise value to determine the corresponding LLR for each received bit (as typically done), the individual noise values are determined according to the instructions herein for each subcarrier or subcarrier. Can be calculated for a group so that a more accurate LLR is generated for each received bit, which is at least partly the frequency of the subcarrier that is received and evaluated over the subcarrier or group of subcarriers where the bit contains the subcarrier Based on.

5, a block diagram of a symbol demodulator 214 is shown in accordance with some embodiments. The symbol demodulator 214 can be, for example, a processing device of the receiver 104. Receiver 104 receives an encoded signal over multiple subcarriers at different frequencies. The signal includes a number of pilot symbols and data symbols modulated on subcarriers using a modulation technique. Referring briefly to FIG. 2, the output of the subcarrier receivers 206, 208, 210, 212 is supplied as an input to the symbol demodulator 214. The symbol demodulator 214 includes a slot deformatter 502, pilot interpolation blocks 504 and 506, a symbol detector block 507, a noise evaluator block 508, an LLR calculator block 510 and an FEC decoder. Block 512.

)을 분리한다. 원 데이터 신호들은 도 1을 참조하여 기술된 바와 같이 QAM 심볼들의 스트림이라 한다. 원 파일롯들/동기화 신호들은 도 1을 참조하여 기술된 바와 같이 QAM 심볼들의 스트림에 삽입된 동기화 심볼들 및 파일롯 심볼들이라 한다. 원 파일롯들/동기화 신호들(

)은 파일롯 보간 블록(504) 및 노이즈 평가기 블록(508)에 전송된다. 파일롯 보간 블록(504)에서, 원 파일롯들 및 동기화 신호들(

)은 각각의 파일롯 심볼 위치에서 채널 응답(

)을 계산하기 위하여 공지된 전송된 파일롯/동기화 심볼과 함께 사용된다. 노이즈 평가기 블록(508)은 파일롯 보간 블록(504)에 의해 생성된 채널 응답 평가값들(

)을 사용하여 각각의 서브캐리어들의 세트에 포함된 서브캐리어들을 통해 수신된 파일롯 심볼들의 적어도 일부와 연관된 노이즈 값을 평가하고, 노이즈 평가 값을 LLR 계산기(510)에 전송한다. 이전에 언급된 바와 같이, 서브캐리어들은 이들의 주파수들에 기초하여 서브캐리어들의 다중 세트로 그룹화되고, 노이즈 값은 방정식(3)을 사용하여 계산될 수 있다.The slot D formatter 502 is the original data signal (d _i) and the original pilot / sync signal based on the mapping of the slot 6 (

). The original data signals are referred to as a stream of QAM symbols as described with reference to FIG. The original pilots / synchronization signals are referred to as synchronization symbols and pilot symbols inserted in the stream of QAM symbols as described with reference to FIG. 1. Original pilots / synchronization signals (

Are transmitted to the pilot interpolation block 504 and the noise evaluator block 508. In pilot interpolation block 504, the original pilots and the synchronization signals (

) Is the channel response () at each pilot symbol position.

Is used in conjunction with the known transmitted pilot / synchronization symbol. The noise evaluator block 508 stores the channel response estimates (generated by the pilot interpolation block 504).

) Is used to evaluate a noise value associated with at least some of the pilot symbols received on the subcarriers included in each set of subcarriers, and transmit the noise evaluation value to the LLR calculator 510. As mentioned previously, subcarriers are grouped into multiple sets of subcarriers based on their frequencies, and noise values can be calculated using equation (3).

)은 파일롯 보간기 블록(506)에 추가로 제공되고 각각의 파일롯 심볼 위치에서 채널 응답(

)을 계산하기 위해 공지된 전송된 파일롯/동기화 심볼 값들과 함께 사용되고, 그 다음 이들 평가값들은 각각의 데이터 심볼 위치에서 유사한 평가값들(

)을 제공하기 위해 보간된다. 각각의 데이터 심볼 순간에서 채널에 대한 평가값(

)은 수신기(

)에서 전송된 심볼의 수정된 평가값을 계산하기 위하여 심볼 검출기 블록(507)의 원 데이터 신호(d_i)에 적용된다. 그 다음 이런 수신된 심볼 평가값(

)은 LLR 계산기(510)에 전송된다. LLR 계산기(510)는 심볼 검출기 블록(507) 및 노이즈 평가 블록(508)의 출력들에 기초하여 LLR 값을 계산한다. LLR은 사용된 변조 기술에 기초하는 방정식들을 사용하여 계산된다. 계산된 LLR 값은 순방향 에러 수정(FEC) 디코더(512)에 수신된 비트들을 디코딩하기 위해 사용된다. FEC 디코더(512)는 LLR 계산기(510)에서 형성된 LLR 값들을 사용하여 다수의 디코딩된 데이터 비트들을 포함하는 디코딩된 신호를 생성한다.Original pilots and synchronization signals (

) Is further provided to the pilot interpolator block 506 and the channel response () at each pilot symbol position.

Is used in conjunction with known transmitted pilot / synchronization symbol values to calculate the < RTI ID = 0.0 >

To interpolate). Evaluation value for the channel at each instant of data symbol (

) Is the receiver (

) Is applied to the original data signal d _i of the symbol detector block 507 to calculate a modified evaluation value of the symbol transmitted in. This received symbol evaluation value is then

) Is sent to the LLR calculator 510. LLR calculator 510 calculates an LLR value based on the outputs of symbol detector block 507 and noise evaluation block 508. LLR is calculated using equations based on the modulation technique used. The calculated LLR value is used to decode the bits received at the forward error correction (FEC) decoder 512. The FEC decoder 512 uses the LLR values formed in the LLR calculator 510 to generate a decoded signal comprising a plurality of decoded data bits.

As noted above, the various embodiments described above provide a method and apparatus for mitigating interference of MCM systems. The calculation of noise estimates is done on a subcarrier basis or in a group of small subcarriers. Noise estimates are used to calculate LLR values that can provide additional information to FEC decoders to improve coding performance. Providing the FEC decoder with a more detailed knowledge of where interference occurs through the calculation of noise estimates for subcarrier units or small groups of subcarriers provides additional information that leads to better correction probability of the received signal. To provide.

In the foregoing specification, specific embodiments have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are included within the scope of the present guidelines. Benefits, advantages, solutions to problems, and any element (s) from which any benefit, advantage, or solution may occur may be an important, required, or essential feature or element of any or all claims. Should not be interpreted as The present invention is defined only by the appended claims and all equivalents of the patented claims, including any corrections made during the pending of this application.

Furthermore, in this document, related terms such as first and second, top and bottom, and the like do not necessarily require or include any actual relationship or order between the entities or acts and do not include one entity from another entity or act. Or can only be used to distinguish between actions. The terms "comprises", "comprising", "has", "having", "includes", "including", "contains", "containing" or any other variation are intended to cover non-exclusive inclusions, so The comprising process, method, article, or apparatus may not include these elements and may include other elements not represented or unique to the process, method, article, or apparatus. An element preceded by "comprises ... a", "has ... a", "includes ... a", "contains ... a" may contain elements without further limitations, processes, methods, It does not preclude the presence of additional identical elements in the object or device. The terms "a" and "an" are defined as one or more unless explicitly stated otherwise herein. The terms “substantially”, “essentially”, “approximately”, “about” or other versions thereof are defined as close to what is understood by one of ordinary skill in the art and in a non-limiting embodiment the term is within 10%, in other embodiments. Within 5%, within 1% in other embodiments, and within 0.5% in other embodiments. The term "coupled" as used herein is defined as a connection, although not necessarily directly and necessarily mechanically. A device or structure that is "configured" in a particular way is configured in at least that way, but may be configured in ways that are not listed.

Some embodiments mitigate interference of the MCM system described herein with respect to microprocessors, digital signal processors, custom processors and field programmable gate arrays (FPGAs), and certain non-processor circuits. One or more general purpose or special purpose processors (or unique stored program instructions, including both software and firmware) that control one or more processors to implement some, most, or all of the functions and apparatus for all of the functions. It will be appreciated that the " processing devices " Non-processor circuits include, but are not limited to, a wireless receiver, a wireless transmitter, signal drivers, clock circuits, power source circuits, and user input devices. As such, these functions may be interpreted as method steps for performing mitigation of interference of the MCM system described herein. Optionally, some or all of the functions may be implemented in a state machine without stored program instructions, or in one or more application specific integrated circuits (ASICs), where each function or some combination of certain of the above functions is custom logic. Is implemented. Of course, a combination of the two methods could be used. Both state machines and ASICs are implemented herein as "processing devices" for the discussion and claim language above.

In addition, an embodiment may be embodied as a computer-readable storage medium having computer-readable code stored thereon for programming a computer (eg, including a processing device) for performing the methods described and claimed herein. have. Examples of such computer-readable storage media include hard disks, CD-ROMs, optical storage devices, magnetic storage devices, read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM). ), EEPROM (electrically erasable programmable read only memory) and flash memory. In addition, despite the considerable effort and many design choices arising, for example, due to available time, current technology, and economic considerations, those skilled in the art have the least experience when guided by the concepts and principles disclosed herein. It is anticipated that the instructions and programs and ICs may be easily generated.

A summary of the disclosure is provided to enable the reader to quickly understand the nature of the disclosed disclosure. Observations are submitted that are not used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various embodiments for the streaming of the present disclosure. This method of disclosure should not be construed as reflecting the intention of the claimed embodiments to require more features than are explicitly recited in each claim. Rather, as the following claims reflect, inventive subject matter remains less than all features of a single disclosed embodiment. Accordingly, the following claims are incorporated into the detailed description, with each claim standing on its own as a claimed subject matter.

Claims (11)

Receiving an encoded signal over multiple subcarriers at different frequencies, the signal comprising a plurality of pilot symbols and data symbols modulated on the subcarriers using a modulation technique; step; Grouping the subcarriers into sets of multiple subcarriers based on their frequencies; For each set, evaluating a noise value associated with at least some of the pilot symbols received on the subcarriers included in the set; And Generating a decoded signal comprising a plurality of decoded data bits using the evaluated noise values. The method of claim 1, Generating the decoded signal includes: Generating a plurality of received data bits from the data symbols, evaluating a bit value for each received data bit and determining a reliability measure associated with the evaluated bit value, wherein the reliability measure comprises: Said function being a function of an estimated noise value corresponding to a set of subcarriers comprising a subcarrier; And Decoding the plurality of received data bits using associated reliability measurements to produce the decoded signal. The method of claim 2, The reliability measure comprises a log-likelihood ratio indicating a confidence measure that the value of the bit evaluated for the received data bit is the actual bit value of the corresponding transmitted data bit. The method of claim 3, wherein The log-likelihood ratio is evaluated using an equation based on the modulation technique used. The method of claim 3, wherein The log-likelihood ratio is given by

Is determined using

Is the log-likelihood ratio, r is the received bits,

Is the estimated noise value. The method of claim 1, Each set of subcarriers comprises at least two subcarriers with adjacent frequencies. The method of claim 1, The noise value is an equation

Is evaluated using

Is the estimated noise value,

Is the size of the transmitted pilot symbol number (i),

Is the channel estimate at the pilot symbol position (i),

Is a constant calculated from the design parameters and N is the total number of pilot symbols used. The method of claim 1, The modulation techniques include binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), minimum-shift keying (MSK), offset quadrature phase-shift keying (OQPSK), and quadrature amplitude modulation (QAM). At least one of the. In a device of a multicarrier modulation (MCM) system, A receiver device for receiving a signal encoded over multiple subcarriers at different frequencies, the signal device comprising a plurality of pilot symbols and data symbols modulated on subcarriers using a modulation technique; And As a processing device, Group the subcarriers into sets of multiple subcarriers based on their frequencies, For each set, evaluate a noise value associated with at least some of the pilot symbols received on the subcarriers included in the set, And use the evaluated noise values to generate a decoded signal comprising a plurality of decoded data bits. The method of claim 9, Wherein the decoded signal is generated using a forward error correction (FEC) decoder that uses a log-likelihood ratio calculated based on noise values evaluated to produce the decoded signal. A computer-readable storage medium having computer-readable code stored thereon for programming a computer to perform a method on an encoded signal received over multiple subcarriers at different frequencies, the signal using a modulation technique. 10. A computer-readable storage medium, comprising a plurality of pilot symbols and data symbols modulated on subcarriers The method is: Grouping the subcarriers into sets of multiple subcarriers based on their frequencies; For each set, evaluating a noise value associated with at least some of the pilot symbols received on the subcarriers included in the set; And Using the estimated noise values, generating a decoded signal comprising a plurality of decoded data bits.

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